1. Field of the Invention
The present invention relates to gas analyzers. More specifically, the present invention is directed to analyzers for determining the calorific content of a combustible gas.
2. Description of the Prior Art
The measurement of calorific content, e.g., BTU content, of a combustible gas such as that supplied for home heating by a public utility, etc., provides a measure of the quality of the gas being supplied and, hence, the appropriate rate or cost for the gas be billed by the public utility to a customer who formerly was charged a rate based simply on a cubic volume of gas consumption. Conventional gas analyzers for determining the composition of an unknown gas have usually involved a variety of time consuming methods. The basic prior art analyzer is known as the Orsat type and is used to absorb the constituent gases one at a time from a gas mixture and to determine the constituent quantities from a resulting decrease in the gas pressure exhibited by the mixture. The resulting gas analysis could be used as a basis for consumer billing. In another apparatus, chromatographic analysis of the gas constituents has been used to compute the actual heating value or calorific content of a combustible gas from the percentage composition of the combustible constituents of the mixture. In still another device, the heat content of the gas has been determined by measuring the amount of heat liberated in burning one cubic foot of the gas in a closed volume at standard conditions of temperature and pressure. The heat so liberated is absorbed by a known quantity of surrounding water, and the subsequent temperature rise of the water is used to calculate the heating value. However, all such prior art devices are wholly impractical for mass installation on-line in gas consumer locations particularly home consumers, since such methods involve expensive instrumentation and considerable labor to perform the measurements and calculations while introducing substantial time delays. Accordingly, it is desirable to have a so-called on-line system which can measure the calorific content of the combustible gas in an unattended location and which is suitable for mass installations. Known gas analyzers of this latter type include ones based on the use of the thermal conductivity of the known gas which gas is analyzed by comparing its rate of thermal conductivity with that of a standard reference gas. Another prior art gas analyzing device uses a catalyzing wire which has its temperature affected by a gas being burned adjacent to the wire to produce an output signal which is used to ascertain the percentage of combustible gas in the gas being tested. An additional group of gas analyzers are based on an optical analysis of the color, etc., of a gas flame to provide a measure of combustible gas content. However, all of these prior art devices have serious shortcomings in providing a rapid and accurate measurement of the calorific content of the combustible gas while utilizing a compact and simple structure suitable for mass production, on-line installation and capable of being used over extended periods of time without significant maintenance.